popular_tags on relation

[jonnysperber]

Calling popular_tags on a model class works flawless, but it seems not possible to call it on a relation or scope.
My model is called business and has (rocket)tags. If I do something like

@businesses = Business.near(lat,lng)

And then call

@businesses.popular_tags

to get the tag_cloud for this subset of entities, i get the following exception:

PGError: ERROR:  subquery has too many columns
LINE 1: ...e_type" = 'Business' AND "taggings"."taggable_id" IN (SELECT...
                                                             ^
: SELECT COUNT(*) FROM (SELECT count("tags"."id") AS tags_count, tags.* FROM "tags" INNER JOIN "taggings" ON "taggings"."tag_id" = "tags"."id" WHERE "taggings"."taggable_type" = 'Business' AND "taggings"."taggable_id" IN (SELECT  businesses.*, 6371.0 * 2 * ASIN(SQRT(POWER(SIN((52.5408134 - businesses.latitude) * PI() / 180 / 2), 2) + COS(52.5408134 * PI() / 180) * COS(businesses.latitude * PI() / 180) * POWER(SIN((13.4155842 - businesses.longitude) * PI() / 180 / 2), 2) )) AS distance, CAST(DEGREES(ATAN2( RADIANS(businesses.longitude - 13.4155842), RADIANS(businesses.latitude - 52.5408134))) + 360 AS decimal) % 360 AS bearing, "businesses"."id" FROM "businesses"  WHERE (6371.0 * 2 * ASIN(SQRT(POWER(SIN((52.5408134 - businesses.latitude) * PI() / 180 / 2), 2) + COS(52.5408134 * PI() / 180) * COS(businesses.latitude * PI() / 180) * POWER(SIN((13.4155842 - businesses.longitude) * PI() / 180 / 2), 2) )) <= 50) ORDER BY distance LIMIT 9 OFFSET 0) GROUP BY "tags"."id", "tags"."name" ORDER BY tags_count desc) tags

The SQL is not correct, because a IN may not have more than one selected attribute. I don't know though how to rewrite the query correctly in the mind of rocket_tag. Any idea? Is this a error at all or am I using rocket_tags incorrectly. There has to be a way to achieve tag_cloud for subsets.